Shipchief-exactly what I was thinking except below 2450 there was no smooth spots at all. It was better when I rotated the prop but still unacceptable with any power or airspeed combo below 2450/2430ish.
I was going to try all the other positions on the crank, with Whirlwinds blessing, (Jeremy at Whirlwind has been great to deal with), but I think I found the problem, or a problem anyway. I’ll have info in a coupIe days. I had to leave on a trip and will do some measuring Monday.

So the cause of all this may be that the face of the crankshaft was not machined straight. Unfortunately I won’t know if this was the issue until the spring but I will be sure to report back. I’ll tell the story so it may help someone

I purchased this engine with a very minor prop strike. It dialed good but I knew I would feel better if I send the crank out so I tore down an engine with 60 hours on it. The shop checked the runout, crack checked it and did the crank gear. That’s it. It all checked perfectly so yellow tagged and back in my hands I built up the motor. A year or two later when I installed it on the airframe I remembered noticing a slight rock to the flywheel, very slight like less than 1/16 inch of movement. If you held the flywheel at the 9 and 3 o’clock positions it had a very slight walk as you put more pressure on one side vs the other. If you held it on with pressure in the center it seemed fine. I assumed I was rocking it off the edge of the crank and still had thousands of hours left to finish the project so that clue went unnoticed. Now when I was getting ready to reinstall the prop the other week, I noticed the rocking again and it occurred to me that this may be the cause. At first I thought the flywheel was hanging up on the radius of the crank snout, there looked to be some marks that indicated this. So I cleared some material off the flywheel and no luck, still rocking. I borrowed a different flywheel and it still did it. With a straight edge I determined that the face of the crank was ground with a slight taper. Now it’s hard to measure because you can’t go across the center of the crank and with a micrometer you can only measure the 1st inch but it appears that the flange is 10-12 thousands thinner at the edge than in the center. Witness marks show the most of the contact between the flywheel and the crank is at the center. I put blue ink on the flywheel and pushed it on square and it showed the same.

This is what I think was going on. When I installed the prop initially the first bolt I probably tightened was at 12 o’clock, easiest to get at. The prop being horizontal at the time, this rotated the prop up, around the blade axis, which is why it measured fine in tracking. The blade angles would have been very slightly different but nothing I could measure. The math shows that the prop dome would have about a .030 runout in this situation. When I flipped the prop around I must have snugged the bolts more evenly and the vibration got better. I do remember one bolt being extremely tight during removal but was much easier to undo when the rest were loosened. So the clues were there I just didn’t think it was possible to have this problem.

Since this discovery I have gotten more sets of eyes on this for confirmation. I have decided that the motor is going out to a reputable shop for tear down and proper machining on the crank. Maybe some HP mods. This was the plan all along as I didn’t want to break in a new engine on a new airframe so at least it did it’s job. Hopefully this solves the problem and I will report back.

All
I have a couple flights on the new engine and all the vibration is gone now. I can’t praise Whirlwinds service enough. They were willing to go above and beyond to fix this. I called ECI to give them the serial # on the crank that may have slipped by. As I was not the original owner I’m not sure how concerned they were. The folks at BPA took care of the engine and it’s what you would expect from them. A great looking and powerful package. Now to continue testing!!

I went through all this with my Laser with a Whirlwind 200AC prop too. Smoother at high rpm and irritating at 2350 rpm cruise. Cleaned and flow checked the injectors, dynamic compression tested, reclocked the prop to match TDC of #1, couldn’t find anything. Switched from new Aircraft Spruce bushings to Lord and that helped. Opened up clearance around the engine and baffling and cowl and that helped. The airplane came with 200C blades but I only had three quick flights with those a year before I flew it again withe 200AC blades so no real comparison. I also switched to the Skydynamics lightweight magnesium flywheel with the 200AC blades.

I think the vibration is down to an acceptable level now. It shows up the most when you take your hand off the stick and you can see it vibrate. A dynamic balancer with spectrum output would have saved me a lot of testing because it isolates the prop imbalance from engine combustion issues. The 200AC blades made a huge difference in my CHTs so I have to believe the cuffs near the spinner are pumping a lot more air into the cowl which may also be felt as vibration. Then too my empty weight is less than a 1000 lbs and I have a pumped up engine with a light prop and flywheel, there’s bound to be some vibration that’s not absorbed by the mount bushings.

I followed your troubles on other forums and tried just about everything as you did. Found the problem and got it fixed. Now fine tuning. I will also do the light weight flywheel soon with rebalancing. So far so good though. Amazing what a proper crank flange will do. I’m at 1030lbs empty but it is what it is. Barrett rebuilt the straight valve 180hp with 9.5 to 1 pistons and it’s very smooth. So on to more testing.

On a side note, I grew up in Detroit and remember you flying a pattern ship at Grosse Ile during a RC event. You did a slow roll that went the length of the runway, AWESOME!!